Existing head-mounted displays (HMDs) use a single focal distance to display digital content. This constraint can make it uncomfortable for a user to look at holograms that are located near the user, but far away from the focal plane, due to a phenomenon known as vergence-accommodation conflict. Additionally, it may be virtually impossible to simultaneously focus on nearby holograms and nearby real-world objects. Variable-focus displays are in development that are able to adjust optical power to match where the user is looking, and multi-focal displays could render each holographic pixel at a different focal distance, enabling users to benefit from a more comfortable and realistic mixed-reality and/or virtual reality experiences.
However, by the age of 55, humans lose the ability to accommodate for nearby objects and must rely on bifocals or progressive lenses to view nearby objects clearly. This condition is known as presbyopia. It may be difficult for users with presbyopia to use and interact with mixed-reality or virtual reality experiences that include holograms that are rendered at nearby focal ranges.